Crowdsourcing work with high levels of coupling between tasks poses challenges for coordination. This paper presents a study of two online citizen science projects that involved volunteers in such tasks: not just analyzing bulk data but also interpreting data and writing a paper for publication in one project and identifying new classes of data in the other. However, extending the reach of citizen science adds tasks with more dependencies, which calls for more elaborate coordination mechanisms but the relationship between the project and volunteers limits how work can be coordinated. Contrariwise, a mismatch between dependencies and available coordination mechanisms can be expected to lead to performance problems. The results of the study offer recommendations for design of citizen science projects for advanced tasks.